A new generation of polyurethane vascular prostheses: Rara Avis or Ignis Fatuus?

Abstract

Three polyurethane (PU) vascular grafts with novel designs were investigated and compared in terms of the microporous structure, reinforcement technology, polymer chemistry, microphase separation, and mechanical properties. The Corvita graft, composed of a poly(carbonate urethane) polymer, displayed a helically wound filament structure with communicating inter-fiber spaces. The reinforced model contained an external PET mesh impregnated with a protein sealant, and displayed good microphase separation, the highest Young's modulus in the longitudinal direction, and the second highest in the radial direction. The Thoratec graft was made of a polyetherurethaneurea with an average micropore size of 15 microns. Silicone was observed on both surfaces of the graft. The Thoratec device displayed a low degree of hydrogen-bonding among the urethane groups and had no well-organized hard-segment domains. Its mechanical strength was superior to that of the Pulse-Tec graft. A solid PU layer underneath the luminal surface precluded any communication between the luminal and adventitial sides. The Pulse-Tec prosthesis was composed of polyetherurethane, with an average micropore size of 28 microns. It offered the highest radial compliance, a high degree of hydrogen-bonding, a narrow molecular weight distribution, and a certain degree of microphase separation. Its tensile strength and hysteresis loss were inferior to those of the other two grafts.

Prosthetic vascular grafts: Wrong models, wrong questions and no healing

“…In fibrillar designs porosity was varied through fibre thickness, winding angle, regularity of the deposition and extent of coagulation of fibres before solidification. With fibre thickness varying between 1 and 30 mm [72,91], for instance, pore sizes could be achieved between 10 and 60 mm [72,[91][92][93]. However, regardless of whether fibrillar grafts were produced through weaving [94,95], knitting [94], electrostatic spinning [91] or winding processes [72,73] the presence of communicating transmural spaces permissible for blood vessel ingrowth was coincidental rather than intentional.…”

“…Phase inversion alone, for example, led to micropores that were generally poorly interconnected and smaller than 15 mm [92,[96][97][98] therefore not allowing more than a shallow, superficial penetration by capillaries. Differences between various phase/temperature inversion techniques [99] allowed some degree of variability in this microporosity.…”

Electrospun vascular grafts with improved compliance matching to native vessels

“…Grafts such as the Corvita ® , Thoratec ® , and PulseTec ® have been developed with modest improvements in compliance but were still lacking compared to autologous standards. 10 Newer commercial SPU grafts such as the UCL-Nano™ and Myolink™ grafts, now available in Europe, have exhibited improved compliance values much greater than traditional synthetic grafts; however, these grafts have no recorded burst pressure exceeding autologous vessels. 11, 12 Due to the highly tunable segmented chemistry, SPUs with a range of mechanical properties and stress responses more closely matching native vessels could be achieved.…”

Mechanical properties of small‐diameter polyurethane vascular grafts reinforced by weft‐knitted tubular fabric

“…However, graft thrombosis is still a serious clinical problem in spite of continuous improvements in grafts and vascular surgery 14. Polyurethane appears to be a satisfactory material to solve the thrombus problem due to its excellent elastic property and the biocompatibility, microporous structure can be successfully fabricated in the wall of the vascular grafts using different methods 15–22. Porosity in the vascular grafts wall can be reduced by coating or sealing with a novel ionic urethane, to improve their blood leakproof property.…”